CN110310887B - Wafer generation method and wafer generation device - Google Patents

Wafer generation method and wafer generation device Download PDF

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Publication number
CN110310887B
CN110310887B CN201910221577.8A CN201910221577A CN110310887B CN 110310887 B CN110310887 B CN 110310887B CN 201910221577 A CN201910221577 A CN 201910221577A CN 110310887 B CN110310887 B CN 110310887B
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wafer
single crystal
ingot
hexagonal single
crystal ingot
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CN110310887A (en
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山本凉兵
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Disco Corp
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Disco Corp
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/03—Observing, e.g. monitoring, the workpiece
    • B23K26/032—Observing, e.g. monitoring, the workpiece using optical means
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/322—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to modify their internal properties, e.g. to produce internal imperfections
    • H01L21/3221—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to modify their internal properties, e.g. to produce internal imperfections of silicon bodies, e.g. for gettering
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02002—Preparing wafers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/0006—Working by laser beam, e.g. welding, cutting or boring taking account of the properties of the material involved
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
    • B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
    • B23K26/0624—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses using ultrashort pulses, i.e. pulses of 1ns or less
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/08—Devices involving relative movement between laser beam and workpiece
    • B23K26/083—Devices involving movement of the workpiece in at least one axial direction
    • B23K26/0853—Devices involving movement of the workpiece in at least in two axial directions, e.g. in a plane
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/36—Removing material
    • B23K26/38—Removing material by boring or cutting
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/50—Working by transmitting the laser beam through or within the workpiece
    • B23K26/53—Working by transmitting the laser beam through or within the workpiece for modifying or reforming the material inside the workpiece, e.g. for producing break initiation cracks
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28D—WORKING STONE OR STONE-LIKE MATERIALS
    • B28D5/00—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor
    • B28D5/0005—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor by breaking, e.g. dicing
    • B28D5/0011—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor by breaking, e.g. dicing with preliminary treatment, e.g. weakening by scoring
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28D—WORKING STONE OR STONE-LIKE MATERIALS
    • B28D5/00—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor
    • B28D5/04—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor by tools other than rotary type, e.g. reciprocating tools
    • B28D5/047—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor by tools other than rotary type, e.g. reciprocating tools by ultrasonic cutting
    • H—ELECTRICITY
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02002—Preparing wafers
    • H01L21/02005—Preparing bulk and homogeneous wafers
    • H01L21/02008—Multistep processes
    • H01L21/0201—Specific process step
    • H01L21/02021—Edge treatment, chamfering
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    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02367—Substrates
    • H01L21/0237—Materials
    • H01L21/02373—Group 14 semiconducting materials
    • H01L21/02378—Silicon carbide
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    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02587—Structure
    • H01L21/0259—Microstructure
    • H01L21/02598—Microstructure monocrystalline
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/67005—Apparatus not specifically provided for elsewhere
    • H01L21/67011—Apparatus for manufacture or treatment
    • H01L21/67017—Apparatus for fluid treatment
    • H—ELECTRICITY
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/67005—Apparatus not specifically provided for elsewhere
    • H01L21/67011—Apparatus for manufacture or treatment
    • H01L21/67092—Apparatus for mechanical treatment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/67005—Apparatus not specifically provided for elsewhere
    • H01L21/67242—Apparatus for monitoring, sorting or marking
    • H01L21/67253—Process monitoring, e.g. flow or thickness monitoring
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/67005—Apparatus not specifically provided for elsewhere
    • H01L21/67242—Apparatus for monitoring, sorting or marking
    • H01L21/67259—Position monitoring, e.g. misposition detection or presence detection
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/77—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate
    • H01L21/78—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L22/00—Testing or measuring during manufacture or treatment; Reliability measurements, i.e. testing of parts without further processing to modify the parts as such; Structural arrangements therefor
    • H01L22/20—Sequence of activities consisting of a plurality of measurements, corrections, marking or sorting steps
    • H01L22/26—Acting in response to an ongoing measurement without interruption of processing, e.g. endpoint detection, in-situ thickness measurement
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2103/00—Materials to be soldered, welded or cut
    • B23K2103/50—Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
    • B23K2103/52—Ceramics
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2103/00—Materials to be soldered, welded or cut
    • B23K2103/50—Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
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Abstract

Provided are a wafer generation method and a wafer generation device, which can easily peel a wafer from a hexagonal single crystal ingot with a peeling layer as a starting point, and can easily judge that the peeling of the wafer from the hexagonal single crystal ingot is completed. The wafer generation method comprises the following steps: a peeling layer forming step of forming a peeling layer (74) by irradiating a hexagonal single crystal ingot (50) with laser light by positioning a Focal Point (FP) of laser Light (LB) having a wavelength that is transparent to the hexagonal single crystal ingot (50) at a depth from an end surface of the hexagonal single crystal ingot (50) that corresponds to the thickness of a wafer to be produced; an ultrasonic wave generation step of positioning an ultrasonic wave generation unit (6) so as to face a wafer to be generated through a water-resistant Layer (LW), and causing the ultrasonic wave generation unit (6) to generate ultrasonic waves to break a release layer (74); and a peeling detection step for detecting peeling of the wafer to be produced from the hexagonal single crystal ingot (50) by positioning the imaging unit (10) on the side surface of the wafer to be produced.

Description

Wafer generation method and wafer generation device
Technical Field
The present application relates to a wafer generation method and a wafer generation apparatus for generating wafers from hexagonal single crystal ingots.
Background
IC. LSI, LED, etc. devices are made of Si (silicon) or Al 2 O 3 (sapphire) or the like is formed by laminating a functional layer on the front surface of a wafer as a raw material and dividing the functional layer by a dividing line. In addition, the power device, the LED, and the like are formed by stacking functional layers on the front surface of a wafer made of single crystal SiC (silicon carbide) and dividing the functional layers by dividing lines. The wafer on which the devices are formed is divided into device chips by processing the lines to be divided by a cutting device or a laser processing device, and the divided device chips are used for electronic devices such as mobile phones and personal computers.
Wafers for device formation are generally produced by slicing a cylindrical semiconductor ingot by a wire saw. The front and back surfaces of the wafer obtained by cutting are polished to mirror surfaces by grinding (for example, refer to patent document 1). However, when a semiconductor ingot is cut by a wire saw and the front and back surfaces of the cut wafer are polished, most (70% to 80%) of the semiconductor ingot is wasted, which is an uneconomical problem. In particular, hexagonal single crystal SiC ingots have problems in that they have high hardness, are difficult to cut by a wire saw, take a relatively long time, and therefore have poor productivity, and in that the hexagonal single crystal ingots have high unit price, and in that they are efficient in producing wafers.
Accordingly, the present inventors have proposed the following technique: a laser beam is irradiated to the hexagonal single crystal SiC ingot by positioning a light-collecting point of a laser beam having a wavelength that is transparent to the hexagonal single crystal SiC in the hexagonal single crystal SiC ingot, and the wafer is peeled from the hexagonal single crystal SiC ingot with the peeling layer as a starting point on a surface to be cut (for example, see patent document 2).
Patent document 1: japanese patent laid-open No. 2000-94221
Patent document 2: japanese patent laid-open publication 2016-111143
However, there are the following problems: it is difficult to peel a wafer from a hexagonal single crystal ingot with the peeling layer as a starting point, and the production efficiency is poor. In addition, there are the following problems: it is difficult to determine whether the detachment of the wafer from the hexagonal single crystal ingot is completed.
Disclosure of Invention
Accordingly, an object of the present application is to provide a wafer generation method and a wafer generation apparatus that can easily separate a wafer from a hexagonal single crystal ingot with a separation layer as a starting point, and can easily determine that separation of the wafer from the hexagonal single crystal ingot is completed.
According to one aspect of the present application, there is provided a wafer producing method for producing a wafer from a hexagonal single crystal ingot, the wafer producing method comprising: a peeling layer forming step of forming a peeling layer by irradiating a hexagonal single crystal ingot with laser light at a depth corresponding to the thickness of a wafer to be produced from an end surface of the hexagonal single crystal ingot by positioning a light-collecting point of the laser light at a wavelength that is transparent to the hexagonal single crystal ingot; an ultrasonic wave generating step of positioning an ultrasonic wave generating means so as to face a wafer to be generated with a water layer interposed therebetween, and generating ultrasonic waves by the ultrasonic wave generating means so as to break the peeling layer; and a peeling detection step of positioning the imaging unit on the side surface of the wafer to be produced and detecting peeling of the wafer to be produced from the hexagonal single crystal ingot.
Preferably, the hexagonal single crystal ingot is a hexagonal single crystal SiC ingot having a C-axis and a C-plane perpendicular to the C-axis, and in the separation layer forming step, a laser beam is irradiated to the hexagonal single crystal SiC ingot by positioning a light-collecting point of a laser beam having a wavelength that is transparent to the hexagonal single crystal SiC at a depth from an end face of the hexagonal single crystal SiC ingot corresponding to a thickness of a wafer to be produced, thereby forming a separation layer composed of a modified portion obtained by separating SiC into Si and C and a crack extending isotropically from the modified portion along the C-plane. Preferably, the hexagonal single crystal ingot is a hexagonal single crystal SiC ingot having a c-axis inclined with respect to a perpendicular to the end face and a drift angle formed between the c-face and the end face, and the separation layer is formed in the separation layer forming step as follows: the modified portion is continuously formed in a direction perpendicular to a direction in which the off angle is formed, a crack extending isotropically from the modified portion along the c-plane is generated, the hexagonal single crystal SiC ingot and the converging point are relatively index-fed in a range not exceeding a width of the crack in the direction in which the off angle is formed, and the modified portion is continuously formed in a direction perpendicular to the direction in which the off angle is formed, and a crack extending isotropically from the modified portion along the c-plane is sequentially generated, thereby forming the peeling layer.
According to another aspect of the present application, there is provided a wafer producing apparatus for producing a wafer from a hexagonal single crystal ingot formed with a peeling layer formed in the following manner: the peeling layer is formed by irradiating a hexagonal single crystal ingot with laser light at a depth from an end surface of the hexagonal single crystal ingot corresponding to a thickness of a wafer to be produced by positioning a light-collecting point of the laser light having a wavelength that is transparent to the hexagonal single crystal ingot, wherein the wafer production apparatus comprises: an ultrasonic wave generating unit having an end face facing the wafer to be generated, the ultrasonic wave generating unit generating ultrasonic waves through a water layer; a photographing unit positioned at a side of a wafer to be generated; and a peeling detecting means connected to the imaging means for detecting peeling of the wafer to be produced from the hexagonal single crystal ingot, based on a change in the interval between the wafer to be produced and the hexagonal single crystal ingot.
According to the method for producing a wafer of the present application, the wafer can be easily peeled from the hexagonal single crystal ingot starting from the peeling layer, and the completion of the peeling of the wafer from the hexagonal single crystal ingot can be easily determined from the change in the height of the upper surface of the wafer to be produced.
According to the wafer generation device of the present application, the wafer can be easily peeled from the hexagonal single crystal ingot starting from the peeling layer, and the completion of the peeling of the wafer from the hexagonal single crystal ingot can be easily determined from the change in the height of the upper surface of the wafer to be generated.
Drawings
Fig. 1 is a perspective view of a wafer generating apparatus according to an embodiment of the present application.
Fig. 2 is a perspective view of a wafer generating apparatus showing a state in which a SiC ingot is held by the ingot holding unit shown in fig. 1.
Fig. 3 (a) is a front view of a SiC ingot, and fig. 3 (b) is a plan view of the SiC ingot.
Fig. 4 (a) is a perspective view showing a state in which a release layer is formed on the SiC ingot shown in fig. 3, and fig. 4 (b) is a front view showing a state in which a release layer is formed on the SiC ingot shown in fig. 3.
Fig. 5 (a) is a top view of a SiC ingot having a release layer formed thereon, and fig. 5 (B) is a cross-sectional view taken along line B-B in fig. 5 (a).
Fig. 6 is a front view of the wafer generating apparatus showing a state in which ultrasonic waves are applied to the SiC ingot.
Fig. 7 (a) is a schematic diagram of a binarized image of an SiC ingot to which an ultrasonic wave front is applied, and fig. 7 (b) is a schematic diagram of a binarized image when the interval between a wafer to be produced and the SiC ingot exceeds a predetermined value.
Fig. 8 is a front view of the wafer creating device showing a state in which the wafer holding member is brought into close contact with the peeled wafer.
Fig. 9 is a front view of a wafer creating apparatus showing a state in which a peeled wafer is sucked and held by a wafer holding member.
Description of the reference numerals
2: a wafer generating device; 6: an ultrasonic wave generating unit; 6a: an end face of the ultrasonic wave generating unit; 10: a photographing unit; 12: a peeling detection member; 50: an ingot; 52: a first end face; 54: a second end face; 58: a perpendicular to the first end face; 70: a modifying section; 72: cracking; 74: a peeling layer; 76: a wafer; alpha: a deviation angle; a: a direction in which a deviation angle is formed; LB: a laser beam; FP: a converging point; LW: an aqueous layer.
Detailed Description
Embodiments of a wafer generating method and a wafer generating apparatus according to the present application are described below with reference to the drawings.
First, an embodiment of the wafer generating apparatus of the present application will be described. The wafer generating apparatus 2 shown in fig. 1 includes: an ingot holding unit 4 that holds a hexagonal single crystal ingot (hereinafter, simply referred to as ingot); an ultrasonic wave generating unit 6 having an end face 6a facing the wafer to be generated, for generating ultrasonic waves through the water layer; a water supply means 8 for supplying water between the wafer to be produced and the ultrasonic wave generation unit 6 to produce a water layer; a photographing unit 10 positioned at a side of a wafer to be generated; a peeling detecting means 12 connected to the imaging means 10 for detecting peeling of the wafer to be generated from the ingot, based on a change in the interval between the wafer to be generated and the ingot; and a wafer holding member 14 for holding the wafers peeled from the ingot.
The ingot holding unit 4 will be described with reference to fig. 1 and 2. The ingot holding unit 4 in the present embodiment includes: a cylindrical base 16; a cylindrical holding table 18 rotatably mounted on the upper surface of the base 16; and a motor (not shown) that rotates the holding table 18 about an axis extending in the up-down direction through the radial center of the holding table 18. The ingot holding unit 4 can hold an ingot fixed to the upper surface of the holding table 18 by an appropriate adhesive (for example, an epoxy-based adhesive). Alternatively, the ingot holding unit 4 may be configured such that a porous suction chuck (not shown) coupled to a suction member (not shown) is disposed at the upper end portion of the holding table 18, and suction force is generated on the upper surface of the suction chuck by the suction member, thereby sucking and holding the ingot.
The wafer generating apparatus 2 in the present embodiment further includes a Y-axis direction moving mechanism 20, and the Y-axis direction moving mechanism 20 moves the ultrasonic wave generating unit 6, the water supply member 8, and the wafer holding member 14 in the Y-axis direction indicated by an arrow Y in fig. 1. The Y-axis direction moving mechanism 20 includes: a rectangular parallelepiped frame 22 having a rectangular guide opening 22a extending in the Y-axis direction; a first ball screw (not shown) extending in the Y-axis direction inside the housing 22; a first moving piece 24 extending from a base end portion coupled to the first ball screw in an X-axis direction indicated by an arrow X in fig. 1; a first motor 26 connected to one end of the first ball screw; a second ball screw (not shown) extending in the Y-axis direction inside the housing 22; a second moving piece 28 extending in the X-axis direction from a base end portion coupled to the second ball screw; and a second motor 30 connected to one end of the second ball screw. The Y-axis direction moving mechanism 20 converts the rotational motion of the first motor 26 into a linear motion by the first ball screw and transmits the linear motion to the first moving plate 24, moves the first moving plate 24 in the Y-axis direction along the guide opening 22a, converts the rotational motion of the second motor 30 into a linear motion by the second ball screw and transmits the linear motion to the second moving plate 28, and moves the second moving plate 28 in the Y-axis direction along the guide opening 22 a. In addition, the X-axis direction is perpendicular to the Y-axis direction, and a plane defined by the X-axis direction and the Y-axis direction is substantially horizontal.
In the present embodiment, as shown in fig. 1, a first elevating member 32 having a cylindrical shape extending downward is connected to the lower surface of the front end of the first moving plate 24, and a cylindrical ultrasonic wave generating unit 6 is connected to the lower end of the first elevating member 32. Accordingly, by moving the first moving sheet 24 in the Y-axis direction, the first elevating member 32 and the ultrasonic wave generating unit 6 are moved in the Y-axis direction. The first elevating member 32 may be constituted by an electric cylinder having a ball screw and a motor, for example. In the first elevating member 32, the ultrasonic wave generating unit 6 is elevated and stopped at an arbitrary position, so that the circular end surface 6a on the lower side of the ultrasonic wave generating unit 6 faces the wafer to be generated. The ultrasonic wave generating unit 6 is formed of piezoelectric ceramics or the like, and generates ultrasonic waves.
As shown in fig. 1, the water supply member 8 includes: a cylindrical connection port 34 attached to the upper surface of the front end of the first movable piece 24; a nozzle 36 supported on the lower surface of the front end of the first movable piece 24 so as to be movable upward and downward; and a nozzle lifting mechanism (not shown) that lifts and lowers the nozzle 36. Therefore, by moving the first moving piece 24, the water supply member 8 is moved in the Y-axis direction. The connection port 34 is connected to a water supply source (not shown) via an appropriate water supply hose (not shown). The nozzle 36 extends downward from the front end lower surface of the first moving plate 24 with a gap in the Y-axis direction from the ultrasonic wave generating unit 6, and then slightly inclines downward toward the ultrasonic wave generating unit 6 and extends in the Y-axis direction. The nozzle 36 is hollow and communicates with the connection port 34. The nozzle lifting mechanism may be constituted by, for example, an electric cylinder, which lifts and lowers the nozzle 36 and stops at an arbitrary position, thereby positioning the outlet 36a of the nozzle 36 between the wafer to be generated and the end face 6a of the ultrasonic wave generating unit 6. The water supply member 8 thus configured supplies water supplied from the water supply source to the connection port 34 from the outlet 36a of the nozzle 36 to between the wafer to be produced and the end face 6a of the ultrasonic wave generating unit 6, and generates a water layer.
In the present embodiment, as shown in fig. 1, the imaging unit 10 is disposed behind the nozzle 36 so that water supplied from the outlet 36a of the nozzle 36 does not splash onto the imaging unit 10, and the imaging unit 10 is supported to be vertically movable by a support bracket (not shown). The imaging unit 10 is lifted and lowered by a lifting structure (not shown) configured by an electric cylinder, and is stopped at an arbitrary position. The photographing unit 10 is positioned on a side surface of the wafer to be formed, and photographs a separation layer formed on the ingot and a gap between the wafer to be formed and the ingot. In addition, the arrangement of the imaging unit 10 may not be the back of the nozzle 36 as long as it is a position where imaging is not hindered by water from the outlet 36a of the nozzle 36. The electrical signal output from the photographing unit 10 is input to the peeling detecting member 12 electrically connected to the photographing unit 10. The peeling detecting member 12 is constituted by a computer, and includes: a Central Processing Unit (CPU) that performs arithmetic processing in accordance with a control program; a Read Only Memory (ROM) which stores a control program and the like; and a read-write-enabled Random Access Memory (RAM) that holds the operation result and the like. In the separation detecting means 12, separation of the wafer to be produced from the ingot is detected based on a change in the interval between the wafer to be produced and the ingot. Specifically, the binarization processing is performed on the image of the ingot 50 captured by the capturing unit 10, and when the interval between the wafer to be generated and the ingot is equal to or more than a predetermined value, it is detected that the wafer is peeled off.
As will be described further with reference to fig. 1, the wafer holding member 14 is connected to the lower surface of the front end of the second moving plate 28, and the wafer holding member 14 is moved in the Y-axis direction by moving the second moving plate 28 in the Y-axis direction. The wafer holding member 14 has: a cylindrical second lifting member 38 extending downward from the lower surface of the front end of the second moving plate 28; and a disk-shaped holding piece 40 connected to the lower end of the second elevating member 38 for sucking and holding the wafer peeled from the ingot. The second elevating member 38 is constituted by, for example, an electric cylinder, and the lower surface of the holding piece 40 is brought into contact with a wafer to be produced by elevating and stopping the holding piece 40 at an arbitrary position. A porous suction chuck (not shown) connected to a suction member (not shown) is attached to a lower end portion of the holding sheet 40. In the wafer holding member 14, the suction force is generated by the suction member on the lower surface of the suction chuck in a state where the lower surface of the holding piece 40 is brought into contact with the wafer peeled from the ingot, so that the wafer peeled from the ingot can be suction-held by the holding piece 40.
An ingot 50 is shown in fig. 3 in a state prior to formation of the release layer. The ingot 50 is formed integrally into a cylindrical shape from hexagonal single crystal SiC, and the ingot 50 has: a first end surface 52 of circular shape; a second end surface 54 having a circular shape on the opposite side from the first end surface 52; a peripheral surface 56 located between the first end surface 52 and the second end surface 54; a c-axis (< 0001 > direction) from the first end face 52 to the second end face 54; and a c-plane ({ 0001} plane) perpendicular to the c-axis. In the ingot 50, the c-axis is inclined with respect to the perpendicular line 58 of the first end surface 52, and a deviation angle α (for example, α=1 degree, 3 degrees, 6 degrees) is formed between the c-plane and the first end surface 52. The direction in which the deviation angle α is formed is indicated by arrow a in fig. 3. Further, a first orientation flat 60 and a second orientation flat 62 having a rectangular shape indicating a crystal orientation are formed on the peripheral surface 56 of the ingot 50. The first orientation plane 60 is parallel to the direction a in which the deviation angle α is formed, and the second orientation plane 62 is perpendicular to the direction a in which the deviation angle α is formed. As shown in fig. 3 b, the length L2 of the second orientation flat 62 is shorter than the length L1 of the first orientation flat 60 when viewed from above (L2 < L1). The ingot from which the wafer can be peeled by the wafer producing apparatus 2 after the peeling layer is formed is not limited to the ingot 50, and may be, for example, a hexagonal single crystal SiC ingot in which the c-axis is not inclined with respect to the perpendicular to the first end surface and the off angle between the c-plane and the first end surface is 0 degrees (that is, the perpendicular to the first end surface coincides with the c-axis), or a hexagonal single crystal ingot formed from a material other than hexagonal single crystal SiC, such as GaN (gallium nitride).
Next, an embodiment of the wafer generation method of the present application will be described. In the present embodiment, first, a peeling layer forming step is performed, in which the laser beam is irradiated to the ingot 50 by positioning the light-collecting point of the laser beam having a wavelength that is transparent to the ingot 50 at a depth corresponding to the thickness of the wafer to be produced from the end surface of the ingot 50, thereby forming the peeling layer. The release layer forming step may be performed using, for example, a laser processing apparatus 64, a part of which is shown in fig. 4. The laser processing device 64 includes: a chuck table 66 for holding a workpiece; and a condenser 68 for irradiating the workpiece held by the chuck table 66 with a pulsed laser beam LB. The chuck table 66 configured to suction and hold the workpiece on the upper surface rotates around an axis extending in the up-down direction by a rotating member (not shown), advances and retreats in the x-axis direction by an x-axis direction moving member (not shown), and advances and retreats in the y-axis direction by a y-axis direction moving member (not shown). The condenser 68 includes a condenser lens (not shown) for converging the pulse laser beam LB oscillated by the pulse laser beam oscillator (not shown) of the laser processing apparatus 64 and irradiating the workpiece with the converged pulse laser beam LB. The x-axis direction is a direction indicated by an arrow x in fig. 4, the y-axis direction is a direction indicated by an arrow y in fig. 4, and the y-axis direction is a direction perpendicular to the x-axis direction. The plane defined by the x-axis direction and the y-axis direction is substantially horizontal. In addition, the X-axis direction and the Y-axis direction indicated by the X and Y of the capital letters in fig. 1 may be identical to or different from the X-axis direction and the Y-axis direction indicated by the X and Y of the capital letters in fig. 4.
In the release layer forming step, first, one end surface (first end surface 52 in the present embodiment) of the ingot 50 is directed upward, and the ingot 50 is sucked and held on the upper surface of the chuck table 66, as described further with reference to fig. 4. Alternatively, an adhesive (for example, an epoxy-based adhesive) may be interposed between the other end surface (in the present embodiment, the second end surface 54) of the ingot 50 and the upper surface of the chuck table 66 to fix the ingot 50 to the chuck table 66. Next, the ingot 50 is photographed from above by a photographing unit (not shown) of the laser processing apparatus 64. Next, based on the image of the ingot 50 captured by the capturing unit, the chuck table 66 is moved and rotated by the x-axis direction moving member, the y-axis direction moving member, and the rotating member of the laser processing apparatus 64, whereby the orientation of the ingot 50 is adjusted to a predetermined orientation, and the positions of the ingot 50 and the condenser 68 on the xy plane are adjusted. When the orientation of the ingot 50 is adjusted to a predetermined orientation, as shown in fig. 4 (a), the second orientation flat 62 is aligned in the x-axis direction in a direction perpendicular to the direction a in which the off angle α is formed, and the direction a in which the off angle α is formed is aligned in the y-axis direction by being aligned with the x-axis direction. Next, the condenser 68 is lifted and lowered by a condenser position adjusting means (not shown) of the laser processing apparatus 64, and as shown in fig. 4 b, the condenser point FP is positioned at a depth (for example, 300 μm) corresponding to the thickness of the wafer to be produced from the first end surface 52 of the ingot 50. Next, a peeling layer forming step is performed, and pulse laser beam LB having a wavelength that is transparent to single crystal SiC is irradiated from the condenser 68 to the ingot 50 while the chuck table 66 is moved at a predetermined feed speed in the x-axis direction aligned with the direction a perpendicular to the direction a in which the off angle α is formed. When the release layer forming process is performed, as shown in fig. 5, the modified portion 70 is continuously formed in a direction perpendicular to the direction a in which the off angle α is formed, and a crack 72 isotropically extending along the C-plane from the modified portion 70 is generated, wherein as the pulse laser beam LB is irradiated, siC is separated into Si (silicon) and C (carbon), and then the irradiated pulse laser beam LB is absorbed by the previously formed C, and SiC is cohesively separated into Si and C, thereby forming the modified portion 70. In addition, in the peeling layer forming process, the condenser 68 may be moved instead of the chuck table 66.
As will be described further with reference to fig. 4 and 5, the chuck table 66 is moved by the y-axis direction moving means continuously after the release layer forming process, and the ingot 50 and the converging point FP are relatively index-fed by a predetermined index amount Li (for example, 250 μm to 400 μm) in a y-axis direction aligned with the direction a in which the off angle α is formed, within a range not exceeding the width of the crack 72. In addition, the condenser 68 may be moved instead of the chuck table 66 at the time of indexing feeding. Further, the peeling layer forming process and the index feed are alternately repeated, whereby a plurality of modified portions 70 continuously extending in a direction perpendicular to the direction a in which the offset angle α is formed are formed at intervals of a predetermined index amount Li in the direction a in which the offset angle α is formed, and cracks 72 extending isotropically from the modified portions 70 along the c-plane are sequentially generated, and the cracks 72 adjacent to each other in the direction a in which the offset angle α is formed overlap with the cracks 72 when viewed from the up-down direction. In this way, the peeling layer 74 composed of the plurality of modified portions 70 and the crack 72 and having a reduced strength for peeling the wafer from the ingot 50 can be formed at a depth from the first end surface 52 of the ingot 50 corresponding to the thickness of the wafer to be produced. The release layer forming step may be performed under the following processing conditions, for example.
After the release layer forming step, an ultrasonic wave generating step is performed, the ultrasonic wave generating means 6 is positioned so as to face the wafer to be generated through the water layer, and the release layer 74 is broken by generating ultrasonic waves by the ultrasonic wave generating means 6. In the ultrasonic wave generating step in the present embodiment, first, as shown in fig. 2, the first end face 52, which is an end face close to the release layer 74, is directed upward, and the ingot 50 is held by the ingot holding unit 4. At this time, an adhesive (for example, an epoxy adhesive) may be interposed between the second end surface 54 of the ingot 50 and the upper surface of the holding table 18 to fix the ingot 50 to the holding table 18, or an attractive force may be generated on the upper surface of the holding table 18 to attract and hold the ingot 50. Next, the first moving plate 24 is moved by the first motor 26 of the Y-axis direction moving mechanism 20, and as shown in fig. 1, the end face 6a of the ultrasonic wave generating unit 6 is brought into face contact with the wafer to be generated (in this embodiment, a portion from the first end face 52 to the peeling layer 74). Next, the ultrasonic wave generating unit 6 is lowered by the first elevating member 32, and when the distance between the first end surface 52 and the end surface 6a of the ultrasonic wave generating unit 6 reaches a predetermined size (for example, about 2mm to 3 mm), the operation of the first elevating member 32 is stopped. The nozzle 36 is moved by the nozzle lifting mechanism, and the outlet 36a of the nozzle 36 is positioned between the first end surface 52 and the end surface 6a of the ultrasonic wave generating unit 6. Next, the holding table 18 is rotated by the motor, and as shown in fig. 6, while the first moving plate 24 is moved in the Y-axis direction by the first motor 26, water is supplied from the outlet 36a of the nozzle 36 between the first end surface 52 and the end surface 6a of the ultrasonic wave generating unit 6, a water layer LW is generated, and the ultrasonic wave generating unit 6 is caused to generate ultrasonic waves. At this time, the holding table 18 is rotated and the first moving sheet 24 is moved in the Y-axis direction so that the ultrasonic wave generating unit 6 passes through the entire first end surface 52, thereby imparting ultrasonic waves to the entire release layer 74. Thus, the peeling layer 74 is broken by transmitting ultrasonic waves to the ingot 50 through the water layer LW, and the wafer 76 to be produced can be peeled from the ingot 50 starting from the peeling layer 74.
In the ultrasonic wave generating step, the frequency of the ultrasonic wave generated by the ultrasonic wave generating means 6 is preferably a frequency near the natural frequency of the ingot 50, and by setting the frequency of the ultrasonic wave in this way, the wafer 76 can be efficiently peeled from the ingot 50 in a relatively short time (about 1 to 3 minutes) even with an ultrasonic wave having a relatively low output (about 200W, for example). The frequency around the natural frequency of the ingot 50 is specifically about 0.8 to 1.2 times the natural frequency of the ingot 50, and is about 20kHz to 30kHz when the natural frequency of the ingot 50 is 25kHz, for example. In addition, even at a frequency exceeding the frequency around the natural frequency of the ingot 50 (in the above example, at a frequency exceeding 30 kHz), the wafer 76 can be efficiently peeled from the ingot 50 in a relatively short time, if an ultrasonic wave having a relatively high output (for example, about 400W to 500W) is used.
In the ultrasonic wave generation step, it is preferable that the temperature of water supplied between the first end surface 52 of the ingot 50 and the end surface 6a of the ultrasonic wave generation unit 6 is set to a temperature at which Cavitation (Cavitation) of the water layer LW can be suppressed when the ultrasonic wave generation unit 6 generates ultrasonic waves. Specifically, the temperature of the water is preferably set to 0 to 25 ℃, so that the ultrasonic energy is not converted into cavitation, and the ultrasonic energy is efficiently transmitted to the release layer 74, thereby efficiently breaking the release layer 74.
As described above, when the ultrasonic wave generation process is performed, the peeling detection process is performed in which the imaging unit 10 is positioned on the side surface of the wafer 76 to be generated, and the peeling of the wafer to be generated from the ingot is detected, and when the peeling detection means 12 detects that the wafer 76 has been peeled from the ingot 50 (when the peeling of the wafer 76 is completed), the ultrasonic wave generation process is ended. In the peeling detecting process of the present embodiment, first, the imaging unit 10 is positioned on the side surface of the wafer 76 to be produced, and the upper end portion of the ingot 50 is imaged by the imaging unit 10. Next, the peeling detecting means 12 performs binarization processing on the image captured by the capturing unit 10, and detects the gap between the wafer 76 to be generated and the ingot 50. Fig. 7 (a) is a schematic diagram showing an image obtained by binarizing an image captured by the imaging unit 10 before ultrasonic waves are applied to the ingot by the peeling detecting means 12. In the image shown in fig. 7 (a), the thickness of the release layer 74 (for example, about 100 μm) is detected as the gap between the wafer 76 to be produced and the ingot 50. When ultrasonic waves are applied to the ingot 50, the peeling layer 74 is broken, and the gap between the wafer 76 to be produced and the ingot 50 is enlarged. When the gap between the wafer 76 to be produced and the ingot 50 is equal to or smaller than a predetermined value (for example, about 400 μm to 500 μm) as a reference of whether the wafer 76 has been peeled from the ingot 50, the peeling detecting means 12 determines that the wafer 76 to be produced is not completely peeled from the ingot 50 (that is, that all or a part of the wafer 76 has not been peeled), and the ultrasonic wave generating process is continued. Then, as shown in fig. 7 (b), when the gap between the wafer 76 to be produced and the ingot 50 is equal to or greater than the predetermined value, the peeling detecting means 12 detects that the wafer 76 to be produced has been peeled from the ingot 50. In the present embodiment, since the holding table 18 is rotated during the ultrasonic wave generating step, the separation detecting means 12 detects the gap between the wafer 76 to be generated and the ingot 50 over the entire circumference of the ingot 50, and detects that all of the wafer 76 to be generated has been separated from the ingot 50 when the detected gap over the entire circumference of the ingot 50 is equal to or greater than the predetermined value. In this way, when the peeling of the wafer 76 to be generated is detected, the ultrasonic wave generating process and the peeling detecting process are ended.
After the ultrasonic wave generating step and the peeling detecting step are performed, the first moving plate 24 is moved by the first motor 26 to separate the ultrasonic wave generating unit 6 and the nozzle 36 from above the ingot 50, and the second moving plate 28 is moved by the second motor 30 to position the wafer holding member 14 above the ingot 50. Next, as shown in fig. 8, the holding piece 40 is lowered by the second elevating member 38, and the lower surface of the holding piece 40 is brought into contact with the first end surface 52. Next, the suction member connected to the holding sheet 40 is operated to generate a suction force on the lower surface of the holding sheet 40, and the peeled wafer 76 is sucked and held by the holding sheet 40. Then, as shown in fig. 9, the holding piece 40 is lifted by the second lifting member 38, and the second moving piece 28 is moved by the second motor 30, so that the peeled wafer 76 is conveyed.
As described above, in the present embodiment, the wafer 76 can be easily peeled from the ingot 50 with the peeling layer 74 as a starting point, and it can be easily determined that the peeling of the wafer 76 from the ingot 50 is completed. In the present embodiment, since the ultrasonic wave generation process is completed when the wafer 76 is peeled off, the time for the ultrasonic wave generation process is not unnecessarily increased, and the productivity can be improved. In the present embodiment, water is supplied from the water supply means 8 between the wafer 76 to be generated and the end face 6a of the ultrasonic wave generation unit 6, so that a water layer LW is generated between the wafer 76 to be generated and the end face 6a of the ultrasonic wave generation unit 6, and ultrasonic waves are transmitted to the ingot 50 through the water layer LW, and therefore the wafer 76 can be peeled from the ingot 50 without using a water tank, and therefore, the time for storing water in the water tank and the amount of water to be used can be saved, which is economical.
In the release layer forming step of the present embodiment, the following examples are described: the modified portion 70 is continuously formed in a direction perpendicular to the direction a in which the offset angle α is formed, and the index feed is performed in the direction a in which the offset angle α is formed, but the direction in which the modified portion 70 is formed may not be a direction perpendicular to the direction a in which the offset angle α is formed, and the direction in which the index feed is performed may not be the direction a in which the offset angle α is formed. In the present embodiment, the first elevating member 32 for elevating the ultrasonic wave generating unit 6 and the nozzle elevating mechanism for elevating the nozzle 36 are described as separate structures, but the ultrasonic wave generating unit 6 and the nozzle 36 may be elevated by a common elevating mechanism provided in the first movable plate 24, or the ultrasonic wave generating unit 6, the nozzle 36, and the wafer holding member 14 may be elevated by elevating the frame 22 of the Y-axis direction moving mechanism 20.

Claims (4)

1. A wafer producing method for producing a wafer from a hexagonal single crystal ingot, wherein,
the wafer generation method comprises the following steps:
a peeling layer forming step of forming a peeling layer by irradiating a hexagonal single crystal ingot with laser light at a depth corresponding to the thickness of a wafer to be produced from an end surface of the hexagonal single crystal ingot by positioning a light-collecting point of the laser light at a wavelength that is transparent to the hexagonal single crystal ingot;
an ultrasonic wave generating step of positioning an ultrasonic wave generating means so as to face a wafer to be generated with a water layer interposed therebetween, and generating ultrasonic waves by the ultrasonic wave generating means so as to break the peeling layer; and
and a separation detecting step of locating the imaging unit on the side surface of the wafer to be produced, imaging the interval between the wafer to be produced and the hexagonal single crystal ingot, and detecting the separation of the wafer to be produced from the hexagonal single crystal ingot.
2. The method for producing a wafer according to claim 1, wherein,
the hexagonal single crystal ingot is a hexagonal single crystal SiC ingot having a c-axis and a c-plane perpendicular to the c-axis,
in this separation layer forming step, a laser beam is irradiated to the hexagonal single crystal SiC ingot by positioning a light-collecting point of a laser beam having a wavelength that is transparent to the hexagonal single crystal SiC at a depth from an end face of the hexagonal single crystal SiC ingot corresponding to the thickness of a wafer to be produced, thereby forming a separation layer composed of a modified portion obtained by separating SiC into Si and C and a crack extending isotropically from the modified portion along the C-plane.
3. The method for producing a wafer according to claim 2, wherein,
the hexagonal single crystal ingot is a hexagonal single crystal SiC ingot having a c-axis inclined with respect to a perpendicular to an end face and an off-angle formed by the c-face and the end face,
in the release layer forming step, the release layer is formed as follows: the modified portion is continuously formed in a direction perpendicular to a direction in which the off angle is formed, a crack extending isotropically from the modified portion along the c-plane is generated, the hexagonal single crystal SiC ingot and the converging point are relatively index-fed in a range not exceeding a width of the crack in the direction in which the off angle is formed, and the modified portion is continuously formed in a direction perpendicular to the direction in which the off angle is formed, and a crack extending isotropically from the modified portion along the c-plane is sequentially generated, thereby forming the peeling layer.
4. A wafer producing apparatus that produces a wafer from a hexagonal single crystal ingot formed with a peeling layer formed in the following manner: the peeling layer is formed by irradiating a hexagonal single crystal ingot with laser light at a depth from an end surface of the hexagonal single crystal ingot corresponding to a thickness of a wafer to be produced, the depth being a distance from a light-condensing point of the laser light having a wavelength that is transparent to the hexagonal single crystal ingot,
the wafer generating device comprises:
an ultrasonic wave generating unit having an end face facing the wafer to be generated, the ultrasonic wave generating unit generating ultrasonic waves through a water layer;
a photographing unit positioned at a side surface of a wafer to be generated, photographing a space between the wafer to be generated and a hexagonal single crystal ingot; and
and a separation detecting means connected to the imaging means for detecting separation of the wafer to be produced from the hexagonal single crystal ingot based on a change in the interval between the wafer to be produced and the hexagonal single crystal ingot.
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